The invention relates to the field of optical signal conditioners, and, specifically, to the art of attenuating optical signals using a saturable absorbing substance.
In recent years, a number of optical fiber systems have been disclosed which replace mechanical and electrical devices. For instance, optical fiber gyroscopes have been developed which provide an accuracy and range comparable to mechanical systems, without requiring the use of moving parts. Optical fiber systems have been used extensively in the field of communications, and are being used increasingly in the field of computations.
One particular use of an optical fiber system is in splice-free optical fiber recirculating memory/delay lines such as described in U.S. Pat. No. 4,373,270, issued on Sept. 25, 1984 and as described in U.S. Pat. No. 3,479,701, issued on Oct. 30, 1984; both of which are incorporated herein by reference. The referenced devices utilize passive optical fiber components to achieve data recirculation within an optical fiber loop. In order to achieve a larger number of recirculations, an amplifier can be inserted into the fiber loop to maintain the recirculating pulses at a usable level. Fiber dispersion and the use of active devices to amplify the signal pulses within the loop can cause distortion of the pulses and can also result in extraneous noise signals, thus resulting in the possible loss of recirculating data. Additionally, amplification of the recirculating signal can result in loss of data by causing the leading and trailing edges of the pulse signal to increase in amplitude, thus broadening the pulse width and therefore reducing the maximum data rate of the recirculating device. Accordingly, there is a need in the art for a signal conditioner which restores the pulse shape after amplification and fiber dispersion and which reduces amplified noise.